Device and method for regulating a spark-ignition gas engine

ABSTRACT

A protective device for a spark-ignition gas engine is provided, which engine has a throttle valve for controlling a gas/air mixture and has an exhaust-gas turbocharger with a turbine that is associated with a throttle member for exhaust gas. A detection unit is configured to detect an actual differential pressure across the throttle valve, and a control unit is configured to change the position of the throttle member based on the actual differential pressure. The throttle member for the exhaust gas is provided only downstream of the turbine in relation to the flow direction of the exhaust gas. A method for regulating an exhaust-gas throttle member, connected downstream of a turbine of an exhaust-gas turbocharger, is also disclosed.

The invention relates to a protective device for a spark-ignition gas engine, having a throttle valve for a gas-air mixture GL and having an exhaust-gas turbocharger which includes a turbine and to which a throttle element for exhaust gas A is associated, wherein a detection unit is provided by which an actual pressure difference Δp across the throttle valve is detectable, and a control unit is provided by which the position of the throttle element is variable as a function of the actual pressure difference Δp.

During the operation of a supercharged spark-ignition engine, in particular of a gas engine with different fuels or mixtures thereof, the charge pressure upstream of the throttle valve varies, while the mixture pressure upstream of the cylinder remains approximately constant when the fuels have different combustion characteristics, such as for example natural gas and biogas. This is because, in the case of gas engines, the exhaust-gas temperature upstream of the turbine of the turbocharger rises due to the different combustion characteristics. As a result, the compressor power also rises, and a higher charge pressure than is necessary is generated.

In the gas engine, an excessively high charge pressure leads to an increase in the pressure difference across the throttle valve, because the pressure required upstream of the cylinder head, or downstream of the throttle valve, for operation at constant power remains approximately constant.

If a threshold value of the pressure difference across the throttle valve is exceeded, the compressor of the turbocharger reaches the surge line. In the case of modern turbochargers with “narrow characteristic maps”, a very high pressure difference leads to “surging”. Surging refers to an instability in the volume flow rate delivered by the compressor, which in turn, due to other side-effects, can lead to system failures and to turbocharger damage and engine damage.

To avoid this, solutions are known which regulate the pressure difference across the throttle valve by using a bypass at the compressor or a bypass at the turbine of the turbocharger.

For example, an internal combustion engine having an exhaust-gas turbocharger is also already known from DE 103 15 148 A1. A bypass line or a bypass, which connects the primary side to the secondary side, is associated with the exhaust-gas turbocharger. To prevent surging of the compressor, it can be equipped with internal recirculation. Recirculation means that air or air mixture is recirculated from the secondary side of the compressor to the primary side of the compressor. This recirculation can also be configured in a switchable manner.

A device for a spark-ignition gas engine is known from DE 10 2009 049 394 A1, which device includes on the one hand a throttle valve as well as a detection unit for the pressure difference across the throttle valve, and on the other hand includes a throttle element in a bypass line of the exhaust-gas turbine for the purpose of regulating the volume flow rate in the bypass line.

The object underlying the invention is to develop and arrange a control device such that surging of the compressor is prevented in a simple manner.

In particular in the case of older engines or engines that were installed without this equipment, in particular without a bypass line, retrofitting is highly cumbersome, expensive and/or impossible, because entire parts of the exhaust system and fresh-air system would have to be newly designed and exchanged.

The object is achieved according to the invention in that the throttle element for the exhaust gas A is provided only downstream of the turbine with respect to the flow direction of the exhaust gas A. A bypass line is not provided. In this case, the detection unit can be reduced to the detection of the pressures or the valve position, wherein the control unit performs the evaluation and/or calculation of the actual pressure difference Δp. The pressures are thus either directly detected or are determined using the position of the throttle valve as a function of the actual pressure difference. The throttle element or the exhaust-gas valve influences the exhaust-gas back pressure at the turbine of the exhaust-gas turbocharger by assuming different positions. By measuring the charge pressure or the mixture pressure upstream and downstream of the throttle valve and/or by detecting the position of the throttle valve, the actual pressure difference across the throttle valve can be directly determined or derived. In a simple controller, the measured pressure difference is compared with a parameterizable and storable target value. In the event of deviations from the target value, an actuating signal is transmitted to the exhaust-gas valve in the exhaust system or to the corresponding actuator until the desired target pressure difference across the throttle valve is achieved. Overall, by throttling, the power of the turbine of the turbocharger can be reduced by a reduced pressure gradient between the inlet and the outlet, and thus also the charge pressure upstream of the throttle valve can be reduced and surging thus prevented.

In this way, damage to the system and to the engine during operation with different fuel qualities and/or gas compositions, or under variable environmental conditions which have an influence on the intake temperature, can be avoided.

This solution can be retrofitted to any system, regardless of engine manufacturer and without intrusion into the engine architecture or the existing engine control regime. The exhaust-gas valve, as a typical throttle element, can be retrofitted in a simple manner. If there is already an exhaust-gas valve for a bypass and/or an exhaust-gas heating boiler system, it is also possible for one of these two throttle elements to be used in accordance with the invention. For this purpose, all that is required is the detection of the actual pressure difference Δp across the throttle valve and corresponding regulation of the throttle element.

It is expedient for the pressure difference across the throttle valve to be taken into consideration for the control and/or the configuration of the exhaust-gas valve.

Adjustable exhaust-gas valves are also suitable for intensely fluctuating environmental conditions such as the intake temperature, because this likewise has a great influence on the charge pressure and/or the pressure difference. The invention thus relates to a protective device for a spark-ignition gas engine, having a throttle valve for gas-air mixture GL and having an exhaust-gas turbocharger which includes a turbine, wherein a throttle element for the exhaust gas A is provided only downstream of the turbine with respect to the flow direction of the exhaust gas A, wherein a detection unit is provided by which an actual pressure difference Δp across the throttle valve is detectable, and a control unit is provided by which the position of the throttle element is variable as a function of the actual pressure difference Δp. The object is also achieved by an exhaust gas system of a spark-ignition gas engine, and by a spark-ignition gas engine having the above-mentioned protective device, as claimed in claims 4 and 5 respectively.

For this purpose, it can also be advantageous if the detection unit includes two pressure sensors P1, P2 for determining the actual pressure difference Δp across the throttle valve or is formed as a sensor unit for determining the position of the throttle valve. The pressure difference across the throttle valve can also be calculated in the control unit and/or the CPU if the individual pressures are measured. This measurement is also possible with a pressure difference sensor. Alternatively, it would also be possible to use the throttle valve position as a measure for the actual pressure difference, i.e. the throttle element or the position of the exhaust-gas valve can also be determined as a function of the opening of the throttle valve, because the degree of opening is dependent on the pressure difference across the throttle valve. In this case, the target value for the regulation is the throttle valve position or the position of the throttle valve actuator, which is detected by the detection unit.

It may furthermore be advantageous if the throttle element includes an actuator and is formed as an exhaust-gas valve or an exhaust-gas slide valve. Typical valves can be easily provided with an actuator, by which the position of the throttle element is variable. The adjustment of the throttle element or the exhaust-gas valve can take place electrically, hydraulically or pneumatically.

Alternatively, it can also be provided that the throttle element is formed as an exhaust-gas aperture. In the case of a known and consistent gas composition and a very constant intake temperature, it is also possible for an exhaust-gas aperture to be provided which is adapted to these conditions, which exhaust-gas aperture is inserted between two flanges of the exhaust-gas system. However, in the event of a significant change in the gas composition, it would have to be exchanged in a suitable manner. The regulating elements and/or control elements are thus not required. The detection of the actual pressure difference is however of importance in any case.

The object is also achieved by a method for regulating an exhaust-gas throttle element, which is connected downstream of a turbine of an exhaust-gas turbocharger, of a spark-ignition gas engine having a throttle valve in the mixture system, wherein the actual pressure difference Δp across the throttle valve is monitored and, in the case of an excessively high pressure difference, the throttle element is partially closed until the actual pressure difference Δp reaches a desired value.

In conjunction with the method according to the invention, it can be advantageous if

-   -   a) a threshold value Δp_tv and/or a target value Δp_target for         the pressure difference Δp across the throttle valve is         predefined;     -   b) the actual pressure difference Δp across the throttle valve         is determined;     -   c) the attainment of the threshold value Δp_tv or a deviation         from the target pressure difference Δp_target is determined;     -   d) the position of the throttle element is varied as a function         of the ratio between the actual pressure difference Δp and the         threshold value Δp_tv or the target pressure difference         Δp_target. A resolution of 50 mbar for the actual pressure         difference Δp with a control frequency of 10/min is adequate         here.

The use of a target value or of a threshold value is discretionary, and these are to be regarded as equivalent. The threshold value is, strictly speaking, nothing other than a target threshold value, upon the attainment of which the regulation of the throttle element commences.

Furthermore, it can also be advantageous if, as an alternative to step d), a fixed or non-variable exhaust-gas aperture is utilized in the exhaust gas system as a throttle element, the opening cross section of which exhaust-gas aperture is, depending on the ratio between the actual pressure difference Δp and the threshold value Δp_tv or the target pressure difference Δp_target, selected to be of such a size that the desired target pressure difference Δp_target across the throttle valve is achieved. In the case of a known and consistent gas composition and a very constant intake temperature, it is also possible for an exhaust-gas aperture to be provided which is adapted to these conditions, which exhaust-gas aperture is inserted between two flanges of the exhaust-gas system. However, in the event of a significant change in the gas composition, it would have to be exchanged in a suitable manner. The regulating elements or control elements are thus not required. The detection of the actual pressure difference is however of importance in any case.

It may also be advantageous if between 50 mbar and 400 mbar, in particular of 300 mbar, is set as the target value Δp_target, and/or a if 200 mbar to 400 mbar is set as the threshold value Δp_tv. The greater the upper threshold value is, the greater is the reserve for load alteration. Equally, the margin with respect to the surge line is correspondingly small. A lower threshold of below 50 mbar has the effect, in practical terms, that the throttle element always remains open.

Further advantages and details of the invention are explained in the patent claims and in the description and are illustrated in the figures, in which:

FIG. 1 shows a diagrammatic sketch of the protective device; and

FIG. 2 shows an alternative embodiment.

A spark-ignition gas engine 2 depicted in FIG. 1 includes an exhaust gas system 2 a having a turbine 2.2 of an exhaust-gas turbocharger 2.5 and a throttle element 2.3 which follows said turbine as viewed in the flow direction of an exhaust gas A. Furthermore, a mixture system 2 b for fresh air L and gas G having a charge-air compressor and/or a mixture compressor 2.4 of the exhaust-gas turbocharger 2.5 is provided, to which a throttle valve 2.1 connects in the flow direction of the gas-air mixture GL. The fresh air L and the gas G are mixed at a mixing point 3.

In the region of the throttle valve 2.1, a detection unit 1.1 having two pressure sensors P1, P2 is provided as part of the protective device 1, by which an actual pressure difference Δp across the throttle valve 2.1, that is to say upstream and downstream of the throttle valve 2.1, is detectable. The actual pressure difference Δp is calculated by a control unit 1.2, such that the position of the throttle element 2.3 is variable by the control unit 1.2 as a function of this actual pressure difference Δp.

For this purpose, the throttle element 2.3 includes an actuator 2.3 a, which functions electrically, hydraulically or pneumatically.

The pressure difference Δp across the throttle valve 2.1 is monitored, wherein, in the case of an excessively high pressure difference Δp, the throttle element 2.3 is partially closed until the pressure difference Δp has fallen to a desired value.

For this purpose, a threshold value Δp_tv and/or a target pressure difference Δp_target for the pressure difference Δp across the throttle valve 2.1 can be predefined for the control unit 1.2, which compares it with the actual pressure difference Δp across the throttle valve 2.1. If the threshold value Δp_tv is attained or if the target pressure difference Δp_target is exceeded, the control unit 1.2 transmits a signal via a control line 1.2 a to the actuator 2.3 a, so that the position of the throttle element 2.3 is thus varied such that the throughflow cross section is reduced, and consequently the exhaust-gas back pressure at the turbine outlet of the exhaust-gas turbocharger 2.5 is increased.

The throughflow cross section of the throttle element 2.3 is accordingly set such that an attainment of the threshold value Δp_tv, or an exceedance of the target pressure difference Δp_target, is prevented.

In FIG. 2, a sensor unit for determining the position of the throttle valve 2.1 is provided as the detection unit 1.1. The presently prevailing actual pressure difference Δp can be derived from the position of the throttle valve 2.1. This is performed by a function stored in the control unit 1.2.

Reference Numeral List

-   1 Protective device -   1.1 Detection unit -   1.2 Control unit -   1.2 a Control line -   2 Spark-ignition gas engine -   2.1 Throttle valve -   2.2 Turbine of 2.5 -   2.3 Throttle element, exhaust-gas valve, exhaust-gas slide valve,     exhaust-gas aperture -   2.3 a Actuator -   2.4 Charge-air compressor and/or mixture compressor -   2.5 Exhaust-gas turbocharger -   2 a Exhaust gas system -   2 b Mixture system -   3 Mixing point -   A Exhaust gas -   Δp Actual pressure difference -   Δp_target Target pressure difference -   Δp_tv Threshold value of the pressure difference -   G Gas -   GL Gas-air mixture -   L Air, fresh air -   P1 Pressure sensor -   P2 Pressure sensor 

1. A protective device for a spark-ignition gas engine, having a throttle valve for a gas-air mixture and having an exhaust-gas turbocharger which includes a turbine, to which a throttle element for exhaust gas is associated, the throttle element for the exhaust gas being provided only downstream of the turbine with respect to a flow direction of the exhaust gas, wherein a detection unit is provided by which an actual pressure difference across the throttle valve is detectable, and a control unit is provided by which a position of the throttle element is variable as a function of the actual pressure difference.
 2. A protective device according to claim 1, wherein the detection unit includes two pressure sensors for determining the pressure difference across the throttle valve or is formed as a sensor unit for determining a position of the throttle valve.
 3. The protective device according to claim 1, wherein the throttle element includes an actuator and is formed as an exhaust-gas valve or an exhaust-gas slide valve.
 4. An exhaust gas system of a spark-ignition gas engine having an exhaust-gas turbocharger which includes a turbine and having a mixture system of a spark-ignition gas engine with a mixture compressor, which is coupled to the turbine, for a gas-air mixture, with a throttle valve which is provided downstream of a mixture compressor with respect to a flow direction, and with a protective device according to claim
 1. 5. A spark-ignition gas engine having an exhaust gas system and having a mixture system according to claim
 4. 6. A method for regulating an exhaust-gas throttle element, connected downstream of a turbine of an exhaust-gas turbocharger, of a spark-ignition gas engine having a throttle valve in a mixture system, comprising monitoring a pressure difference across the throttle valve and, if the pressure difference equals or exceeds a predetermined amount, partially closing the throttle element until the pressure difference has fallen to less than the predetermined amount.
 7. The method according to claim 6, including a) predefining a threshold value and/or a target value for the pressure difference across the throttle valve; b) determining the actual pressure difference across the throttle valve; c) determining the attainment of the threshold value or a deviation from the target pressure difference; and d) varying a position of the throttle element as a function of a ratio between the actual pressure difference and the threshold value or the target pressure difference.
 8. The method according to claim 7, including, as an alternative to step d), utilizing an exhaust-gas aperture in the exhaust gas system as a throttle element, the opening cross section of which exhaust-gas aperture is selected, based on the ratio between the actual pressure difference and the threshold value or the target pressure difference, to be of such a size that the desired pressure difference across the throttle valve is achieved.
 9. The method according claim 6, wherein the target value is between 50 mbar and 400 mbar, and/or the threshold value is 200 mbar to 400 mbar.
 10. The protective device according to claim 1, wherein the throttle element comprises a valve.
 11. The method according claim 9, wherein the target value is 300 mbar.
 12. An exhaust system for a spark-ignition gas engine comprising: a first path carrying exhaust away from the spark-ignition gas engine; a second path carrying a gas-air mixture to the spark-ignition gas engine; a turbine in the first path having a turbine inlet and a turbine outlet; a throttle element in the first path downstream of the turbine outlet; a compressor in the second path operatively connected to the turbine; a throttle valve in the second path between the compressor and the spark-ignition gas engine; a detector configured to produce an output indicative of an actual pressure difference across the throttle valve; and a controller operatively connected to the detector and to the throttle element, the controller being configured to control the position of the throttle element based on the output of the detector.
 13. The exhaust gas system according to claim 12, wherein the throttle element comprises a valve.
 14. The exhaust gas system according to claim 12, wherein the detector comprises a first pressure sensor in the second path upstream of the throttle valve and a second pressure sensor in the second path downstream of the throttle valve.
 15. The exhaust gas system according to claim 12, wherein the detector comprises a sensor for measuring a position of the throttle valve.
 16. The exhaust gas system according to claim 12, wherein the throttle element comprises a valve and the detector comprises a first pressure sensor in the second path upstream of the throttle valve and a second pressure sensor in the second path downstream of the throttle valve.
 17. The exhaust gas system according to claim 12, wherein the throttle element comprises a valve and the detector comprises a sensor for measuring a position of the throttle valve. 